The present invention relates to terminal devices, and more particularly to a terminal device for reading cartographic files from an internal storage device in which the cartographic files are stored as digital data generated about individual units defined by dividing a map into a plurality of regions.
(First Background Art)
Recently, an increasing number of vehicles are carrying navigation systems. Early navigation systems were only provided with files for generating maps on a screen (hereinafter referred to as cartographic files). However, recent models can be supplied not only with the cartographic files but also with traffic information and route guide information. Supply of such various information has made the car navigation systems so convenient that they are expected to rapidly prevail more and more.
The earlier navigation systems were equipped with storage devices having read-only storage media such as CD-ROMs. Cartographic files to be provided to users and their relevant data are previously recorded in the storage media. The storage devices read the cartographic files recorded in the storage media when necessary. The read cartographic files are referred to by the users, or used in route search or map matching process.
Generally, in order to efficiently manage a hierarchical structure of maps on different scales, a map is equally divided into rectangular areas in the longitude and latitude directions and a digital cartographic file is generated for each rectangular area. Now, in First Background Art, such a rectangular area is called a unit.
Such cartographic files are used in the car navigation systems typically for the route search process or process of correcting the present position (map matching). The cartographic files therefore contain road network data. The road network data is at least composed of connection information showing connections among nodes and links. Generally, a node is a piece of information which represents an intersection in the road network, and a link is vector information which represents a road between two intersections. A collection of such nodes and links expresses a map which shows the road network in each unit.
While minimum details of the road network can be represented with the nodes, links and their connection information, it is not enough for the purpose of displaying a map. For example, most roads in mountain or seaside areas are curved between intersections. Therefore the road network data further contains information for specifying the link shape to display curved roads. As is clear from this, the links are often represented by vector data.
Further, the roads include various types, such as national roads, prefectural roads, etc. The roads can be classified also according to the number of lanes, whether it has a median strip, etc. The road network data therefore also contains attribute information which shows the road type and the like.
Some intersections have their own names and others don""t. Further, some intersections have traffic signals and others don""t. Therefore the road network data further contains attribute information for each node. Each piece of the attribute information contains information showing the name of the intersection, presence/absence of traffic signals, etc.
When a road extends over a plurality of units in a cartographic file having the vector data structure, special nodes are separately generated at the boundary between the units (referred to as neighboring nodes hereinafter). The connection of a road can be traced between the neighboring units via the neighboring nodes. To specify the correspondence between a neighboring node of a unit and a neighboring node of a neighboring unit, the conventional cartographic files contain their offset addresses and record numbers. The offset address shows the address location of the neighboring node on the basis of a reference address. The record number shows where the neighboring node is recorded, counted from the first node in the cartographic file of the neighboring unit.
(Second Background Art)
As has been explained in First Background Art, the earlier conventional navigation systems could only use the cartographic files recorded in read-only recording media, so that it was difficult to provide them with real-time information. Typical examples of such real-time information include the traffic and weather information. A map providing system which can provide such real-time information and the cartographic files is disclosed in xe2x80x9cJapanese Patent Laid-Open Publication No.7-262493xe2x80x9d, for example. In the map providing system of this reference, the cartographic files and real-time information are downloaded from an information providing center to a terminal device carried on a car through a communication medium.
The map providing system is constructed on the basis of the mobile communication technology and digital broadcast technology to provide information in real time. In such a map providing system, the center station distributes information to a moving body in the service area by using a given broadcast channel. The center station is typically a communication satellite (so-called CS), a broadcasting satellite (so-called BS), or a ground wave digital broadcast station. A map providing system using the mobile communication technology and digital broadcast technology is disclosed in xe2x80x9cJapanese Patent Laid-Open Publication No.7-154350xe2x80x9d, for example. More specifically, this reference discloses technical contents for limiting the broadcast area for certain information. That is to say, when a center station sends multiplexed information through a broadcast medium, it attaches an area code, like a postal code, to each e of information. A terminal device previously records, in a memory, as an ID, the area code corresponding to its present position. In the terminal device, a data extracting circuit separates the multiplexed information sent from the broadcast station and extracts the area code attached to each piece of the information. The extracted area codes are compared with the recorded ID in the terminal device. When the two agree, the terminal device allows the user to refer to the information having the object area code.
As can be seen from the description above, map providing systems which provide maps through communication or broadcast are being intensively developed in these years. In such a map providing system, a center station reads out target cartographic files by the unit and sends them to a terminal device. The terminal device receives the cartographic data from the center station and stores it in the storage device. The stored cartographic file is used as needed, for user""s reference, route search process, or map matching process.
(Problems of the First Background Art)
In the conventional systems, as is clear from the description in First Background Art, a cartographic file of a unit contains information which directly specifies the internal data structure of cartographic files in the neighboring units (the aforementioned offset addresses or record numbers).
For example, when a new road has been constructed in a unit, the cartographic file of this unit is updated, as a matter of course. In the updated cartographic file, the positions of the neighboring nodes have often been changed. Then, in the conventional method using information directly specifying the internal data structure of the cartographic files, it is impossible to correctly trace from a neighboring node recorded in a cartographic file of a neighboring unit to the corresponding neighboring node in the updated cartographic file. That is to say, updating one cartographic file often requires updating the cartographic files of its neighboring units.
Measures for evaluating the quality of the aforementioned digital cartographic files include the degree to which they give the details of the map. However, since the links are represented by vector data in the cartographic files, representing a more detailed map increases the amount of data of the cartographic file.
Such cartographic files have conventionally been used mainly in the car navigation systems. In the car navigation systems, the cartographic files are recorded in large-capacity storage media such as CD-ROMs, DVD-ROMs, hard disks, etc. However, in the future, the cartographic files will be used not only in the car navigation systems but also in portable information devices. It is difficult to equip such portable information devices with such large-capacity storage media as are used in the car navigation systems. In this respect, there is an intensive demand for compression of the amount of data of the cartographic files.
(Problems of the Second Background Art)
By the way, the references cited in Second Background Art do not disclose how the terminal device stores the cartographic files in the storage device. A likely method is that the terminal device generates a cartographic file for each unit received and stores the genera ted cartographic files in the storage device. However, this method is disadvantageous in that the storage region cannot be efficiently used. For example, as shown in FIG. 71, suppose that a map xcex2 representing an area is sectioned into 64 rectangular units. Also suppose that the terminal device receives four units 71 to 74 and stores them. As is well known, the storage region in the storage device is managed in clusters; where the data size of each unit does not always agree with an integral multiple of the cluster size. Therefore, when the terminal device generates four files 81 to 84 for the received four units 71 to 74, then, as shown in FIG. 72, some areas will be possibly left unused in the four clusters 91 to 94. In FIG. 72, the dotted parts are regions where the files 81 to 84 have been recorded. The hatched parts show the vacant areas. The vacant areas left in the clusters 91 to 94 are not used. That it to say, even when the terminal device receives a unit 75 other than the units 71 to 74 (see FIG. 71), the file generated on the basis of this unit 75 is not stored in the vacant areas in the clusters 91 to 94. As is clear from this, a larger number of clusters will be left not completely filled as the terminal device receives a larger number of units. That is, the efficiency of use of the storage region is lowered.
When the map is divided into a relatively small number of units, the clusters will be less likely to be left partly unfilled. For example, suppose that the map xcex2 covering the area of FIG. 71 is sectioned into 16 rectangular units as shown in FIG. 73. The area represented by the unit 76 of FIG. 73 corresponds to the area covered by the units 71 to 74 in FIG. 71. Also suppose that the terminal device receives and stores one unit 76. Under this assumption, when the terminal device generates one file 86 for the one unit 76, then a vacant area is left only in one cluster 96 as shown in FIG. 74. The dotted part in FIG. 74 shows the area where the file 86 has been recorded. The hatched part shows the vacant area.
As is clear from this, when the map is sectioned into smaller units (see FIG. 71) and cartographic files representing a certain area are stored in the storage device, then relatively large vacant areas are formed in the storage device (see FIG. 72). However, when the map is sectioned into larger units (see FIG. 73), a smaller vacant area is left even when the cartographic data covering the same area is stored in the storage device (see FIG. 74). That is to say, considering the effective use of the storage region, it is desirable to section the map into a less number of units.
However, sectioning the map into a less number of units means a larger amount of data in each unit. Therefore the base station must transmit a larger amount of data at one time to the terminal device. As a result the wireless transmission path will become more susceptible to congestion; that is, this causes another problem that the wireless transmission path cannot be used efficiently. That is to say, while giving priority to the effective use of the storage region reduces the efficiency of use of the wireless transmission path, giving priority to the effective use of the wireless transmission path reduces the efficiency of use of the storage region.
Accordingly, a first object of the present invention is to provide a data structure of the cartographic files in which updating one cartographic file does not require updating cartographic files of the neighboring units. A second object of the present invention is to provide a data structure of the cartographic files in which the amount of data can be compressed. A third object of the invention is to provide a map providing system which can efficiently use the storage region of the terminal device and can also efficiently use the transmission path between the center station and the terminal device.
An aspect of the invention is directed to a terminal device for reading a cartographic file from a storage device in which cartographic files are stored as digital data generated for individual units formed by dividing a map into a plurality of areas, wherein each unit contains a road network represented by nodes and links, and each cartographic file comprises node records generated for respective nodes and link records generated for respective links, and the node records each contain information about a non-neighboring node representing an intersection on the road network or information about a neighboring node defining a connection of roads between its unit and another unit adjoining the unit, the information about the neighboring node being coordinate information about the neighboring node, and wherein the terminal device comprises: an input device responsive to an operation by a user, for generating information specifying a map area; a data processing portion for specifying a record region where a necessary cartographic file is stored on the basis of the information generated by the input device; and a read control portion for reading the cartographic file from the storage device on the basis of the record region specified by the data processing portion, and wherein the data processing portion performs a given process by using the node records and the link records recorded in the cartographic file read by the read control portion, and the data processing portion traces a connection from a road in one unit to a road in another neighboring unit on the basis of the coordinate information about the neighboring nodes of said one unit and the neighboring another unit.
According to the aspect above, during route search, the data processing portion traces the connection of road extending from one unit into a neighboring unit on the basis of coordinate information about the neighboring nodes of the unit and the neighboring unit. In this way, the data processing portion can trace the connection of road between two units without referring to information which directly specifies the internal data structure in the cartographic files. Accordingly, when a cartographic file of a unit in the storage device has been updated, it is not necessary to update cartographic files of the neighboring units.
Another aspect is directed to a terminal device for reading a cartographic file from a storage device in which cartographic files are stored as digital data generated for individual units formed by dividing a map into a plurality of areas, wherein each cartographic file stored in the storage device is provided with a file name uniquely corresponding to the map area represented by itself, and the terminal device comprises: an input device responsive to an operation by a user, for generating information specifying a map area; a data processing portion for specifying a record region where a necessary cartographic file is recorded on the basis of the information generated by the input device; and a read control portion for reading the cartographic file from the storage device on the basis of the record region specified by the data processing portion.
According to the aspect above, each cartographic file is provided with a file name which uniquely specifies the map area it represents. This allows the data processing portion to identify neighboring cartographic files from their names. In this way, according to this aspect, it is not necessary to record any information which is related to the data structure of cartographic files of the neighboring units, so that the plurality of cartographic files are remotely related. Therefore, updating one cartographic file does not require updating other cartographic files.
A further aspect is directed to a terminal device for reading a cartographic file from a storage device in which cartographic files are stored as digital data generated for individual units formed by dividing a map into a plurality of areas, wherein each unit contains a background which is divided into objects each capable of being drawn with one stroke, and the plurality of objects are grouped so that ones having the same attribute are contained in the same group, and the cartographic file contains background records in which information about the objects is recorded for each group, and wherein the terminal device comprises: an input device responsive to an operation by a user, for generating information specifying a map area; a data processing portion for specifying a record region where a necessary cartographic file is stored on the basis of the information generated by the input device; a read control portion for reading the cartographic file from the storage device on the basis of the record region specified by the data processing portion; and an output device; and wherein the data processing portion causes the output device to display the background on the basis of the background records contained in the cartographic file read by the read control portion.
According to the aspect above, in a cartographic file, objects having the same attribute are recorded together in the same background record, which eliminates the need to redundantly record the information about the attribute and thus enables reduction in the amount of data in each cartographic file.
Another aspect is directed to a terminal device for reading a cartographic file from a storage device in which cartographic files are stored as digital data generated for individual units formed by dividing a plurality of maps on different scales each into a plurality of areas, wherein the plurality of cartographic files have a hierarchical structure based on the scales, each unit contains a road network represented by nodes and links, and each cartographic file at least contains node records which are generated for respective nodes and contain coordinate information about the nodes, and link records which are generated for respective links, and in each cartographic file, the node records are recorded in an ascending or descending order of the coordinate information about the nodes, and wherein the terminal device comprises: an input device for generating information specifying a map area; a data processing portion for specifying a record region where a necessary cartographic file is recorded, on the basis of the information generated by the input device; and a read control portion for reading the cartographic file from the storage device on the basis of the record region specified by the data processing portion; and wherein the data processing portion searches for a node in a unit at a higher level which corresponds to a node contained in a unit at a lower level on the basis of the coordinate information recorded in the cartographic file read by the read control portion.
According to the aspect above, the data processing portion retrieves a node in a higher-level unit which corresponds to a node contained in a lower-level unit on the basis of the node coordinate information, i.e. the coordinate information recorded in the cartographic file read by the read control portion. In this way, the data processing portion can trace nodes having the same coordinates between different levels without the need to refer to any information which directly specifies the internal data structure in the cartographic files. Therefore, updating a cartographic file of a unit contained in the storage device does not require updating the cartographic files of the neighboring units.
A further aspect is directed to a system in which a center station provides a cartographic file to a terminal device through a transmission path, wherein the center station comprises: a first storage device containing the cartographic file, the cartographic file representing a map of a predetermined area, a read control portion for reading, as cartographic data, part or all of the cartographic file from the first storage device; a packet assembler for assembling packets in a form appropriate for the transmission path by using the cartographic data read by the read control portion; and a transmitting portion for transmitting the packets assembled by the packet assembler to the terminal device through the transmission path; and wherein the terminal device comprises; a receiving portion for receiving the packets transmitted by the transmitting portion through the transmission path; a data processing portion for disassembling the packets received by the receiving portion and restoring the cartographic data; and a second storage device having an internal storage medium for storing a cartographic file; wherein when a cartographic file related to the cartographic data restored this time is already stored in the second storage device, the data processing portion reads that cartographic file from the second storage device; and the data processing portion performs the process of adding the restored cartographic data to the second cartographic file thus read and storing the cartographic file in the second storage device.
According to the aspect above, the data processing portion combines together the currently restored cartographic data and the cartographic file read from the second storage device and stores it into the second storage device, thereby updating the cartographic file. In this way, the data processing portion generates a cartographic file not only on the basis of the cartographic data received at the receiving portion. The data processing portion adds the currently received cartographic data to the currently read cartographic file. Thus the second storage device stores not a large number of cartographic files containing small amounts of data but cartographic files containing substantial amounts of data, which prevents formation of vacant areas in the clusters. This realizes a map providing system which can effectively utilize the storage region in the terminal device.
Furthermore, according to the aspect above, even if the center station transmits small-sized cartographic data, the terminal device organizes the cartographic data from the center station into one file to suppress formation of vacant areas in the clusters. In this way, since the center station can send small-sized cartographic data, the transmission path is less apt to be congested. This realizes a map providing system which can efficiently utilize the transmission path.